NEET 2023 Chemistry Activation Energy Assertion Reason Question

Explanation of the Question

Assertion A: A reaction can have zero activation energy.
Reason R: The minimum extra amount of energy absorbed by reactant molecules so that their energy becomes equal to the threshold value is called activation energy.

To evaluate the correctness of Assertion A and Reason R, we need to understand the concept of activation energy.

Activation Energy

Activation energy (denoted as $E_a$) is defined as the minimum energy that must be provided for a chemical reaction to occur. It is the energy required to initiate a reaction by allowing reactant molecules to reach the transition state.

In general, for most reactions, activation energy is a positive value, as reactants need to overcome an energy barrier to form products. However, there are specific instances where reactions can indeed have zero activation energy.

Examples of reactions with zero activation energy include:

• Reactions occurring in certain catalytic processes, where the catalyst provides an alternative pathway with no energy barrier.
• Spontaneous reactions that might occur at equilibrium where the reactants can convert to products without needing additional energy (often at very high temperatures).

Evaluating the Statements

1. Assertion A is True: It is possible for a reaction to occur without any activation energy under specific conditions.

2. Reason R is True: The definition provided is correct. It accurately describes what activation energy represents.

Conclusion on Correct Answer

Since both Assertion A and Reason R are true, but Reason R does not provide a correct explanation for Assertion A (because it describes activation energy generally, without addressing the specific case of zero activation energy), the correct answer is:

Correct Answer: A - Both A and R are true and R is NOT the correct explanation of A.

Clarification of Other Options

1. Option B (A is true but R is false): This is incorrect because Reason R is true as it correctly defines activation energy.

2. Option C (A is false but R is true): This is incorrect because Assertion A is true; reactions can indeed have zero activation energy.

3. Option D (Both A and R are true and R is the correct explanation of A): This is incorrect because, while both statements are true, Reason R does not explain why A can be true. R provides a general definition that does not encompass the specific case of zero activation energy.

Summary

• Assertion A is true: A reaction can have zero activation energy.
• Reason R is true but not a correct explanation for A: It describes activation energy without addressing the special case of zero activation energy.
• Therefore, the answer is A: Both A and R are true and R is NOT the correct explanation of A.